Glass-ceramics in the SiO2—Al2O3—Li2O system are characterized by low thermal expansion over a wide temperature range and silica concentrations. These glass-ceramics have a β-quartz solid solution or a β-spodumene solid solution as a main crystalline phase. The β-spodumene phase is known to be mechanically strong with near zero thermal expansion. High mechanical strength and low thermal expansion combined with other properties such as low dielectric loss make these glass-ceramics suitable for consumer electronics and other technical applications. The glass-ceramics are typically white in color or transparent. Consumer electronics applications typically require materials with color variation within a short range.
Glass-ceramics are formed by controlled nucleation and crystallization of glass having a desired composition. Nucleation involves heating the glass to a nucleation temperature and allowing the glass to soak at the nucleation temperature, during which crystal nuclei develop in the glass. Crystallization involves further heating the glass to a crystallization temperature and allowing the glass to soak at the crystallization temperature, during which crystals grow and precipitate in the glass. The resulting glass-ceramic is then cooled to room temperature. The properties of the glass-ceramic will depend on the glass composition, the nucleation and crystallization parameters, and the glass-ceramic microstructure.
Conventional techniques for producing glass-ceramics use resistive heating furnaces for both nucleation and crystallization. The total processing cycle normally takes from 7 to 10 hours when resistive heating is used for nucleation and crystallization. Aside from long processing times, resistive heating requires substantial input energy. With resistive heating, the processing chamber has to be maintained at a uniform temperature to minimize variations in color and microstructure of the glass-ceramic. This means that much of the input energy is directed to heating the volume of the processing chamber that is not occupied by the glass being processed. Where furniture is used to support several samples inside the processing chamber, i.e., for high volume production, substantial energy is also lost to heating of the furniture.